1. Field of the Invention
The present invention relates to an adjustable guide to position a portion of a pipe string within a pipe gripping assembly, such as an elevator assembly or a spider. The present invention relates to an adjustable guide to steer a pipe end into the bottom of an elevator assembly or to generally center a pipe connection so that it may pass through a spider on a drilling rig.
2. Background of the Related Art
Wells are drilled into the earth's crust and completed to establish a fluid conduit between the surface and a targeted geologic feature, such as a formation bearing oil or gas. Pipe strings used to drill or complete a well may be made-up as they are run into a drilled borehole. A casing string may be cemented into a targeted interval of a drilled borehole to prevent borehole collapse and/or formation fluid cross-flow, and to isolate the interior of the well from corrosive geologic fluids.
Generally, a pipe string may be suspended in a borehole from a rig using a pipe gripping assembly called a spider, and step-wise lengthened by threadably joining a pipe segment (which, for purposes of this disclosure, may be a pipe stand comprising a plurality of pipe segments) to the proximal end of the pipe string at the rig. The lengthened pipe string may then be suspended using a second type of gripping assembly called an elevator assembly that is movably supported from a draw works and a derrick above the spider. As the load of the pipe string is transferred from the spider to the draw works and the derrick, the spider may be unloaded and then disengaged from the pipe string by retraction of the spider slips. The lengthened pipe string may then be lowered further into the borehole using the draw works. The spider may again engage and support the pipe string within the borehole and an additional pipe segment may be joined to the new proximal end of the pipe string to further lengthen the pipe string.
Lengthening a pipe string generally involves adding one pipe segment at a time to an existing pipe string. Using one method, a pipe segment is secured to a lift line that hoists the pipe segment into the derrick to dangle the distal end of the pipe segment near the proximal end of the pipe string just above the spider. The distal end of the pipe segment may be, for example, an externally threaded male connection, or “pin end,” of the pipe segment, and it may be positioned by rig personnel to be received into and bear against the proximal end of the pipe string that is suspended by the spider. The proximal end of the pipe string may be, for example, an internally threaded female connection, or a “box end” connection.
A stabber is a member of the rig crew that works in the derrick. The stabber may be secured to a structural component of the derrick to prevent him from falling as he leans out to manually position the proximal end of the pipe segment (which may be an internally threaded connection) to align the distal end of the pipe segment with the proximal end of the pipe string. A power tong may be used to grip and rotate the pipe segment about its axis to make-up the threaded connection between the distal end of the pipe segment and the proximal end of the pipe string to thereby lengthen the pipe string. The proximal end of the now-connected pipe segment then becomes the new proximal end of the lengthened pipe string.
After threadably connecting the pipe segment to the pipe string, the stabber may then align the new proximal end of the pipe string with the inlet of a bell guide that is coupled to the bottom of an elevator assembly. The stabber attempts to position the proximal end of the pipe string to enter the inlet of the bell guide as the elevator assembly is controllably lowered toward the spider using the draw works. After the proximal end of the pipe string passes through the bell guide and then exits the bell guide at its outlet, the proximal end of the pipe string may then enter a bore between the outlet of the bell guide and the gripping zone of the elevator assembly. Further lowering of the elevator assembly will then cause the proximal end of the pipe string to enter and pass through the gripping zone defined by the slips within the elevator assembly.
After the proximal end of the pipe string is received through the gripping zone of the elevator assembly, the elevator assembly slips may be actuated to engage and grip the pipe string just below its proximal end. Subsequently raising the elevator assembly using the draw works lifts the pipe string and unloads the spider. The draw works may then be used to controllably lower the elevator assembly toward the spider to position the proximal end of the pipe string just above the gripping zone of the spider. The spider may reengage and support the pipe string to strategically position the proximal end of the pipe string to receive and threadably connect to a new pipe segment. This step-wise method of lengthening a pipe string is repeated until the pipe string reaches its desired length.
Most gripping assemblies include a tapered bowl having a stepped profile. A stepped profile tapered bowl may comprise a stepped or variable profile within the tapered bowl to provide a generally staged convergence of the slips on the exterior surface of the pipe string. The initial stage of convergence may be a rapid radial convergence of the slips on the exterior surface of a pipe string, generally followed by a more gradual convergence as the slips engage, tighten and grip the exterior surface of the pipe string. While the stepped-profile design affords a more vertically compact elevator assembly, it also substantially limits the range of pipe diameters that may be gripped by the gripping assembly. Pipe strings are generally uniform in diameter and wall thickness throughout their length because gripping assemblies are generally adapted to grip only one size of pipe. Some geological formations, such as salt zones or unconsolidated formations, are prone to movement relative to adjacent formations, and this relative movement may necessitate the use of stronger, thicker-walled pipe at critical intervals to prevent unwanted pipe string failures. Other formations may present a more corrosive environment, thereby necessitating a thicker-walled pipe string. One method of protecting the well against damage in these critical formations is to form the entire pipe string using the thicker and more expensive pipe, but this approach results in a substantial increase in cost.
An alternative method is to install a tapered pipe string, which is a pipe string that has one or more outer pipe diameter transitions along its length. For example, a tapered pipe string may have a first portion with a first pipe wall thickness and outside diameter, and a second portion with a second pipe wall thickness and outside diameter. The second portion of the tapered pipe string may be connected to extend the length of the tapered pipe string beyond the length of the first portion. A tapered pipe string may be installed in a well so that a thicker and stronger-walled portion of the tapered pipe string is strategically positioned within a more critical depth interval of the well. For example, but not by way of limitation, a thicker-walled first portion may be disposed within a tapered pipe string nearer to the surface so that the lower, thinner-walled second portion of the tapered pipe string will be adequately supported by the stronger first portion. As another example, but not by way of limitation, a thicker-walled second portion may be positioned adjacent to an unconsolidated formation or an unstable formation penetrated by the well to ensure that the tapered pipe string offers more resistance to movement or shear as a result of movement in the unconsolidated or unstable formation.
Using conventional, stepped profile tapered bowls, forming a tapered pipe string normally requires the use of two or more elevator assemblies and two or more spiders so that two or more diameters of pipe can be made-up and run in a single pipe string. This approach requires rig downtime to change out the elevator assembly or the spider, or both, for each outer diameter transition.
A different type of tapered bowl for a gripping assembly may comprise a tapered bowl having a smooth and non-stepped profile. FIGS. 1A and 1B illustrate the cross-section of a tapered bowl 120 of a elevator assembly or a spider 110 having a non-stepped profile. For illustration purposes, FIG. 1A shows a spider adapted for being supported from a rig floor, but it should be understood that the same mechanical cooperation and relationship between a tapered bowl and a set of slips may exist in a conventional string elevator, a casing running tool (CRT), or other pipe gripping apparatus having a non-stepped profile.
FIG. 1A shows a set of slips 122 positioned within the tapered bowl 120 to grip a pipe string 188 having a first diameter D1. The slips 122 may be positioned using a timing ring 118 that may be vertically movable, e.g., using extendable rods 119.
FIG. 1B shows the same set of slips 122 positioned vertically higher within the same tapered bowl 120 to grip a second, larger diameter portion of the same pipe string 188 having a diameter D2. These figures illustrate how a smooth, non-stepped profile tapered bowl may be used to run a first portion of a tapered pipe string having a first diameter and to run a second portion of the tapered pipe string having a second diameter without rig downtime to replace the elevator assembly or the spider.
A tapered bowl having a non-stepped profile enables the gripping assembly to engage and grip a range of pipe diameters. The “gripping zone,” as that term is used herein, may be defined as the space within the tapered bowl and between the angularly distributed arrangement of slips, and it varies in size and shape according to the vertical elevation of the set of slips within the tapered bowl when they are engage and grip the pipe.
A limitation that may affect the utility of a spider, elevator assembly (e.g., string elevator, CRT) or other pipe gripping assembly (for example, one having a non-stepped profile) is the difficulty of positioning the proximal end of the pipe string within the gripping zone of the gripping assembly. Wear, warping and material imperfections in the pipe segments or connections may cause the pipe string to be non-linear. Imperfections in the derrick and/or the rig floor, and other factors such as wind and thermal expansion may all combine to cause the bore of the elevator assembly to be misaligned with the proximal end of the pipe string, or to cause the bore of the spider to be misaligned with a pipe connection within the pipe string. For these reasons, the rig crew often has to manually position the proximal end of a pipe string to enter the elevator assembly or to position a pipe connection towards the center of the bore of the spider. It is important that the slips of the tubular gripping apparatus, for example a spider, CRT or elevator assembly, engage and set against the exterior surface of the pipe string as simultaneously and evenly as possible to prevent damage to equipment or to the pipe string, and to ensure a positive grip.
Devices have been developed to assist the rig crew in aligning the proximal end of the pipe string with the elevator assembly. For example, a conventional bell guide is a rigid and generally inverted, funnel-shaped housing that may be coupled to the bottom of an elevator assembly and used to engage and steer the proximal end of the pipe string into the bore of the tapered bowl beneath the gripping zone of the elevator assembly. As the elevator assembly is lowered over the pipe string, the proximal end of a pipe string may engage the sloped interior surface of the bell guide. The reaction force imparted to the proximal end of the pipe string by the bell guide has a compressive component and a radial component. As the elevator assembly is lowered, the proximal end of the pipe string may slide along the interior surface of the bell guide until it reaches the outlet of the bell guide, enter the bore of the tapered bowl of the elevator assembly, and then pass through the gripping zone of the elevator assembly defined by the retracted slips.
A conventional bell guide may have a significant limitation when used with a elevator assembly with a smooth, non-stepped tapered bowl adapted for gripping a broad range of pipe diameters. The size of the outlet of the bell guide must necessarily be larger than the largest diameter of pipe that can be gripped by the elevator assembly. If the outlet of the bell guide is too small to pass the largest pipe diameter that may be gripped by the elevator assembly, then the bell guide may need to be replaced in order to make-up and run a large diameter pipe string. Depending on its capacity, an elevator assembly may weigh up to 15,000 pounds or more, and the bell guide alone may weigh hundreds of pounds. Replacing the bell guide may be difficult and time consuming. Similarly, a bell guide sized to accommodate a large-diameter pipe string may not be useful for running a smaller diameter pipe string. If the outlet at the proximal end of the bell guide is too large, then a smaller diameter pipe string may not be sufficiently aligned by the bell guide with the bore of the gripping zone in the tapered bowl of the elevator assembly as it exits the bell guide, and the proximal end of the pipe string may enter the elevator assembly and hit the bottom of one or more slips as the elevator assembly is lowered over the proximal end of the pipe string.
A bottom guide is another tool that may cooperate with a bell guide and a elevator assembly to position the end of the pipe string to enter the elevator assembly. The bottom guide may be coupled between the outlet of a bell guide and the bore in the bottom of the tapered bowl to receive the end of the pipe string as it passes the bell guide and to further direct it to the bore of the tapered bowl. In one embodiment disclosed in the parent application from which this application depends, a bottom guide may comprise a plurality of replaceable inserts to cooperate with a bell guide and to provide a second convergent structure to position the proximal end of a pipe string within the gripping zone of the elevator assembly. A bottom guide has the same limitation as a bell guide when used with elevator assemblies with tapered bowls having a non-stepped profile. That is, the bottom guide may require adjustment or retro-fitting when the pipe diameter being run into the borehole is changed.
A spider, like an elevator assembly, may also include a tapered bowl having a smooth, non-stepped profile that enables the spider to grip and support a broader range of pipe diameters. Unlike a elevator assembly, a spider does not typically receive the end of a pipe string (except on the very first pipe segment used to begin the string), but it may receive and pass internally threaded pipe sleeves of the kind used to form conventional threaded pipe connections. Each internally threaded sleeve comprises a downwardly disposed shoulder that may be, depending on the diameter and grade of the pipe string being formed, up to 0.30 inches or more in thickness. Misalignment of a pipe connection as it passes through the tapered bowl of the spider may result from the same material imperfections, winds and thermal expansion or contraction, that affect alignment between the bore of the gripping zone of a elevator assembly and the proximal end of the pipe string. A misaligned pipe connection may cause the sleeve to hang on the top of one or more slips or other structures of the spider as the lengthened pipe string is lowered into the borehole using the draw works. Given the large weight of a pipe string, hanging a sleeve shoulder on a spider slip as the pipe string is lowered through the spider may damage the spider, the pipe connection, or both.
A gripping assembly capable of gripping and supporting a broad range of pipe string diameters without alignment problems would provide a significant advantage because it could be used to make-up and run tapered pipe strings, or pipe strings having a generally telescoping configuration, into a borehole with less rig downtime. But misalignment problems caused by material imperfections in pipe, the derrick and other rig structures, and winds and thermal expansion or contraction, make it difficult to achieve the full benefit of using gripping assemblies with tapered bowls having non-stepped profiles. While some tools exist to center the proximal end of a pipe string or a pipe connection, these conventional tools limit the range of diameters of pipe that may be run, thereby defeating the advantage provided by the use of a gripping assembly having a tapered bowl with a non-stepped profile.
What is needed is an adjustable guide that can be coupled to an elevator assembly to position the proximal end of a pipe string relative to the bore of the elevator assembly, and that can be used to position pipe strings within a range of pipe string diameters. What is needed is an adjustable guide that can be coupled to a spider to position a pipe connection relative to the bore of the spider, and that can be used to position pipe connections within a range of pipe connection diameters. What is needed is an adjustable guide that may be used to radially position the proximal end of a pipe string as the elevator assembly is lowered over the proximal end of the pipe string, and that can be used to position pipe strings having a range of diameters. What is needed is an adjustable guide that may be used to radially position a pipe connection within a pipe string as the pipe string is lowered through the spider, and that can be used to position pipe connections having a range of diameters.